Device for tensioning a preform

ABSTRACT

An apparatus for tensioning a preform may include a mandrel to receive a preform. The mandrel may have a first mandrel end and a second mandrel end. The preform may have a first preform end and a second preform end. The apparatus may include an anchoring groove disposed at the first mandrel end, and an anchoring device being configured and located to urge the first preform end towards the anchoring groove to secure the first preform end therebetween. The apparatus may include a tensioning groove disposed between the first mandrel end and the second mandrel end, and a tensioning device being configured and located to urge at least a portion of the preform into the tensioning groove.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a divisional application of and claimspriority to U.S. application Ser. No. 11/633,075 filed on Dec. 4, 2006and entitled TENSIONING DEVICE FOR COMPOSITE STRUCTURES, now U.S. Pat.No. 8,303,757, the entire contents of which is expressly incorporated byreference herein.

FIELD

The disclosure relates generally to a tensioning device for compositematerial component formation and more particularly to a tensioningsystem and device for forming tensioned reinforcement materialcomponents.

BACKGROUND

Generally, in composite frame fabrication, a fiber preform or layup isprepared. A selected plurality of tackified cloth, dry cloth or prepreglaminae may be superimposed or stacked together to provide a preform ofa member, part, or component. The preform is then debulked andimpregnated, if dry or tackified cloth, prior to final curing underpressure. This can be accomplished by using a pressure bag in which thepreform is encased, typically in a vacuum bag. In order to maintain thepreform in a desired shape, the preform can be secured to a rigid,appropriately shaped mandrel, sometimes called a preform tool, frame, ora fixture. This can occur prior to enclosure in a vacuum bag or otherenclosure. The impregnated preform may be cured at room temperature ormay be placed in an oven or autoclave which applies pressure to thepreform through the bag under curing temperature.

During fabrication of these composite parts, it is often the case thatexcess axial fiber length develops into an aberration or wrinkle in thecomposite material layup or preform during compaction or debulking ofthe layup or preform. This is especially true when using braided orwoven materials like two-dimensional (“2D”) and/or three-dimensional(“3D”) 5-harness and/or 8-harness fabrics or braids in plain or diamondpatterns Aberrations can include, at least, warping, wrinkling,undulations, slippage, bends, or the like in the layup that mayadversely affect the appearance of the resulting components.

Many of the previously known methods for anchoring preforms useanchoring portions that are raised or provided as separate parts of amore elaborate, multi-part tool. The clamping mechanism in these devicestypically remains with the tool during the cure cycle. Additionally,these multi-part tools often fail to evenly compress the preform alongthe length of the mandrel. For example, caul plates are often utilizedto compress the preform on to the mandrel. Unfortunately, near the edgesor interface between the caul plates, pressure inconsistencies ormisalignments may occur. This results in dimensional inaccuracies, addeddefects and aberrations, additional resin bleed, increased toolmaintenance and higher operating costs.

Additionally, in most instances only the outermost layers of thelaminate may be extended and gripped by the anchor and the resultingouter layer tensioning may be done by the vacuum bag itself, when thevacuum may be applied. This results essentially in tensioning only onthe outer layer. With these methods tensioning may be applied by plybridging when the vacuum bag forces outer plies which may be cut longerinto a void created by the inner plies being cut shorter and the areabetween the longer plies and the tool is thus “bridged” to apply thetension on the lower plies. Thus, tension may not be applied throughoutthe layers. Moreover, in addition to the added complexities of themulti-part tools noted above, the likelihood of failures due to bagruptures may be increased and the resulting part can be dangerouslyflawed.

Accordingly, it is desirable to provide a layup tensioning device andmethod that is capable of overcoming the disadvantages described hereinat least to some extent.

SUMMARY

The foregoing needs are met, to a great extent, by at least oneembodiment of disclosure, wherein one aspect of the apparatus includes aframe braid tensioning device providing support along the entirety of abraided composite preform and necessary tension to remove excess braidlength through the layers of the preform. An embodiment is provided thathas, for example, a tensioning groove and tensioning mechanism totension the layers of the preform layup and, thus, remove aberrationsthat may occur, essentially to “pull out” aberrations.

An embodiment relates to an apparatus for preparing a preform. Theapparatus includes a mandrel, anchoring groove, anchoring device,tensioning groove, and tensioning device. The mandrel receives thepreform. The mandrel has a first mandrel end and a second mandrel end.The preform has a first preform end and a second preform end. Theanchoring groove is disposed at the first mandrel end. The anchoringdevice is configured and located to urge the first preform end towardsthe anchoring groove to secure the first preform end therebetween. Thetensioning groove is disposed between the first mandrel end and thesecond mandrel end. The tensioning device is configured and located tourge at least a portion of the preform into the tensioning groove.

Another embodiment pertains to a composite curing mandrel. The compositecuring mandrel includes a surface, a plurality of anchors, acorresponding plurality of anchor clamps, a tensioning groove, and atensioning device. The surface receives a layered preform. The surfacehas a first surface end, a second surface end, and a surface width. Thelayered preform has a first preform end, a second preform end, and apreform width. The plurality of anchoring grooves spans the surfacewidth. A first anchoring groove of the plurality of anchoring grooves isdisposed at the first surface end. A second anchoring groove of theplurality of anchoring grooves is disposed at the second surface end.The corresponding plurality of anchor clamps are configured and locatedto secure the first preform end and the second preform end respectivelyto the first surface end and the second surface end. The tensioninggroove is disposed between the first surface end and the second surfaceend and spans the surface width. The tensioning device is configured andlocated to urge a portion of the preform into the tensioning groove toincrease an amount of tension in the layered preform between theplurality of anchoring grooves.

Yet another embodiment relates to a composite tensioning device. Thedevice includes a mandrel, wire, and tensioning device. The mandrelreceives a preform. The wire is coupled to an end of the preform. Thetensioning device is coupled to the wire. The tensioning device isconfigured to draw the wire from the preform to increase an amount oftension in the preform.

Yet another embodiment pertains to a method of fabricating a compositeitem. In this method, a preform is positioned on a mandrel, the preformis anchored to the mandrel, and the preform is urged into a tensioninggroove with a tensioning device to increase an amount of tension in thepreform.

Yet another embodiment relates to a method of fabricating a compositeitem. In this method, a plurality of composite layers is laid on amandrel. The composite layers have a first end and a second end. Inaddition, the first end is fastened to the mandrel, a tensioning deviceis coupled to the second end, and tension is applied to the compositelayers.

There has thus been outlined, rather broadly, certain embodiments inorder that the detailed description thereof herein may be betterunderstood, and in order that the present contribution to the art may bebetter appreciated. There are, of course, additional embodiments thatwill be described below and which will form the subject matter of theClaims appended hereto.

In this respect, before explaining at least one embodiment in detail, itis to be understood that the embodiments are not limited in itsapplication to the details of construction and to the arrangements ofthe components set forth in the following description or illustrated inthe drawings. The disclosure may have embodiments in addition to thosedescribed and of being practiced and carried out in various ways. Also,it is to be understood that the phraseology and terminology employedherein, as well as the abstract, are for the purpose of description andshould not be regarded as limiting.

As such, those skilled in the art will appreciate that the conceptionupon which this disclosure is based may readily be utilized as a basisfor the designing of other structures, methods and systems for carryingout the several purposes of the disclosure. It is important, therefore,that the Claims be regarded as including such equivalent constructionsinsofar as they do not depart from the spirit and scope of thedisclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective illustration of a tensioning mandrelillustrating steps in a method of tensioning a preform of an embodiment.

FIG. 2 is a detailed cross-sectional illustration of a tensioningmandrel and layup.

FIG. 3 is a perspective illustration of a tensioning mandrel of anotherembodiment.

FIG. 4 is a perspective illustration of a tensioning mandrel of anotherembodiment.

FIG. 5 is a side illustration of a tensioning mandrel of anotherembodiment.

FIG. 6 is a perspective illustration of a tensioning mandrel of anotherembodiment.

FIG. 7 is a detailed cross-sectional illustration of a tensioningmandrel and layup of FIG. 6.

DETAILED DESCRIPTION

The embodiments will now be described with reference to the drawingfigures, in which like reference numerals refer to like partsthroughout. An embodiment in provides an apparatus that includes amandrel, an anchoring groove and an anchoring device cooperativelycoupled to the anchoring groove, and a tensioning groove and atensioning device cooperatively coupled to the tensioning groove. Theanchoring groove and anchoring device anchors a layered preform to themandrel and the tensioning groove and tensioning device applies tensionthroughout all the layers in the layered preform.

It is an advantage of various embodiments that sufficient tension may beapplied in a preform to remove wrinkles or similar aberrations from thelayup. It is an additional advantage that tension may be applied tointernal or underlying layers and/or external layers of the preform orlayup. Furthermore, embodiments may be performed economically during thefabrication process. It is another advantage that a single mandrel maybe configured to provide support for the preform. It is yet anotheradvantage of an embodiment that bulk or similar aberrations may beremoved from the composite. These and other attributes of variousembodiments may be especially beneficial in developing curved shapes. Inaddition, anchoring and tensioning devices of the various embodimentsmay be used to hold and support the preform and to provide tension inthe outer layer and/or underlying layers before and/or during a vacuumdebulking process. In some embodiments, the anchor and/or tensiondevices may be applied over, and hence through the pressure or vacuumbag. This may facilitate removal of the anchor and/or tension devicesprior to curing, so as to reduce resin bleed and tool maintenance costs.The apparatus may include a one part tool, resulting in less complicatedtooling, less resin bleed, and improved dimensional accuracy. Theseembodiments may reduce costs associated with tool maintenance andcomposite item fabrication. The tensioning device of various embodimentsmay be equally effective for autoclave and atmospheric pressure cures.

An embodiment of the apparatus and method is illustrated in FIG. 1. Inthe embodiment of FIG. 1, a mandrel 10 (e.g., layup tool, frame, mold,or the like), includes a preform 100 applied thereon. The mandrel 10 maybe a single piece mandrel 10 providing support through the entirety ofthe preform 100. The preform 100 may include any suitable material.Suitable examples of materials include fibers, foils, film, anycombination thereof, and/or the like. The fibers may be dry and/orpre-impregnated with resin and may be arranged in any suitable mannersuch as, for example, unidirectional tape, woven fabrics, 2D and 3Dbraids, and the like. More particularly, suitable braids include, forexample, 5-harness and 8-harness fabric or diamond and/or regularbraids. In this instance, for example, the preform 100 is shown as abraided or near net form layer placed on the mandrel 10 prior toimpregnation with resin. Suitable examples of composite materialsinclude dry and pre-impregnated layers of foils, fibers, films, and thelike. In another example, FIG. 2 shows the preform with several layers101, 102, 103, 104, 105 in place prior to impregnation with a resin.

As shown in step 1 of FIG. 1, the preform 100 may be positioned on themandrel 10 and, optionally, enclosed within a pressure or vacuum bag 60.For example, the preform 100 may be placed upon the mandrel 10 and mayextend substantially from one end of the mandrel 10 to the other end.

As shown in step 2 of FIG. 1, the ends of the preform 100 may be securedto respective ends of the mandrel 10. For example, to secure the preform100 to the mandrel 10, the mandrel 10 may include an anchoring groove 50which accommodates an anchoring device 30, a tapered block and clamp forexample. Optionally, the mandrel 10 may include another anchoring groove52 and another anchoring device 32 and/or a block 54 and clamp 34 (shownin FIG. 2) to secure a distal end of the preform 100 to the mandrel 10.The preform 100 and/or vacuum bag 60 may be disposed between theanchoring device 30 and the anchoring groove 50 and the anchoring device30 may be urged by a clamp or actuator towards the anchoring groove 50to secure the preform 100 and/or vacuum bag 60 therebetween.

As shown in step 3 of FIG. 1, aberrations may, optionally, beidentified. For example, the preform 100 may be compressed by drawing avacuum within the vacuum bag 60 to identify a visible aberration “A.”Following identification, the vacuum may be released to facilitatetensioning at step 4. Of note, the aberration “A” may be formed and/oridentified at essentially any point in the fabrication process. Specificexamples of steps that may be prone to aberration formation includeduring layup of the preform 100 and during debulking or compaction viathe vacuum bag 60 for example.

As shown in step 4 of FIG. 1, the preform 100 may be tensioned or drawntaut to remove wrinkles or other such aberrations. To draw the preform100 taut, the mandrel 10 may include a tensioning groove 40 andtensioning device 20. The tensioning device 20 may include, for example,a tapered block that essentially spans the width of the preform 100and/or tensioning groove 40. The tensioning device 20 may furtherinclude a clamp or actuator 28 to urge the tensioning device 20 towardsthe tensioning groove 40. To tension the preform 100, the preform 100and/or vacuum bag 60 may be disposed between the tensioning groove 40and tensioning device 20 and the tensioning device 20 may be urged bythe actuator 28 towards the tensioning groove 40 to draw at least aportion of the preform 100 and/or vacuum bag 60 into the tensioninggroove 40. As shown in step 4 of FIG. 1, excess material of the preform100 that formed the aberration A in step 3 is drawn towards thetensioning groove 40 when some portion of the preform 100 is drawn intothe tensioning groove 40. In this manner, movement of the tensioningdevice 20 towards the tensioning groove 40 stretches out, draws taut, orotherwise may aid in removing the observed and/or unobservedaberrations, voids, wrinkles, and the like from the preform 100.Alternatively, the vacuum bag 60 may be extended inclusively over thetop of the anchoring device 30 and/or tensioning device 20 withoutdeparting from the spirit of this disclosure.

An example embodiment of a cross-sectional detailed view of the mandrel10 and preform 100 is shown in FIG. 2. The preform 100 may be laid up onthe mandrel 10, or other suitable layup tool, for instance. FIG. 2 showsthe mandrel 10 as being generally curved. However, in other examples,the mandrel 10 need not be curved or may be curved or twisted in anysuitable manner. In a particular example, the mandrel 10 may be curvedat a radius of about 75 inches to about 360 inches. In other examples,the mandrel 10 may include any curve suitable to fabricate a framingmember of an aircraft fuselage. The preform 100 is shown inside thevacuum bag 60. At a first or proximal end, the preform layers 101-105may be anchored by the anchoring device 30 and anchoring groove 50. Inaddition, a distal end of the preform 100 may be secured to the mandrel10 by the block 54 and clamp 34. In this regard, the block 54 and clamp34 and the anchoring device 30 and 32 and anchoring groove 50 and 52 maybe generally described as fasteners. That is, for example, the block 54and clamp 34 function together to fasten or secure the preform 100 tothe mandrel 10 in a similar manner as the anchoring device 30 andanchoring groove 50. Additionally, the embodiments are not limited tothe block 54 and clamp 34 and the anchoring device 30 and 32 andanchoring groove 50 and 52, but rather, any suitable fastener may beincluded in various embodiments. Suitable fasteners include, at least,clamps, presses, and the like. Furthermore, suitable fasteners mayinclude affixing, chemical or heat welding, and the like.

The preform layers 101-105 may include any suitable composite materialsuch as braided preforms, layers of prepreg, foil, film, fabric,unidirectional tape, and the like or any combination thereof. FIG. 2shows a single tensioning device 20 and tensioning groove 40 which doesnot limit the number of tensioning devices 20 or grooves 40 that may beutilized nor does the incorporation of either element in the mandrel 10limit the respective tensioning device or groove from being incorporatedin a multi-part mandrel 10.

The tensioning groove 40 and the preform layers 101-105 may be engagedby the tensioning device 20, here shown as a tapered block and clamp.Clamping layers 101-105 into the tensioning grooves applies tensionforces substantially across the cross section of the preform 100 and thepreform layers 101-105. This effectively “pulls” excess material out ofthe preform 100 and stretches out or draws taut wrinkles or otheraberrations.

It is an advantage of this and other embodiments of the disclosure thatthe tension generated by the tensioning device 20 and tensioning groove40 may be essentially spread through the preform 100. As a result, thepreform 100 may be drawn down onto the mandrel 10. Furthermore, inlayered preforms 100, each layer 100-105 of the preform 100 may besubjected to essentially the same tension which may reduce internalaberrations.

Also shown in FIG. 2, a net trim line 70 and 72 indicate net ends of acomposite item 80. That is, following resin infusion and/or resincuring, the composite item 80 may be generated by cutting or trimming atthe net trim lines 70 and 72.

FIG. 3 is a perspective view of the tensioning mandrel 10 of anotherembodiment. As shown in FIG. 3, the mandrel 10 includes the tensioningdevice 20 and tensioning groove 40 and another tensioning device 22 andtensioning groove 42. In this regard, the mandrel 10 may include anysuitable number of tensioning devices and tensioning grooves. Inaddition, these tensioning devices and tensioning grooves may be locatedanywhere between the fastened ends of the preform 100.

The mandrel 10 shown in FIG. 3 is essentially flat or straight. However,in other examples, the mandrel 10 need not be flat, but rather, may bendor curve in one or more axis. In this regard, the mandrel 10 of FIG. 2is shown to curve along one axis. In other examples, the mandrel 10 maycurve in two axes, such as an arc or segment of a cone. In yet otherexamples, the mandrel 10 may curve, bend, and/or twist in one, two, orthree axes. Furthermore, the curves may be irregular, compound, and thelike.

FIG. 4 is a perspective view of the tensioning mandrel 10 of anotherembodiment of the disclosure. As shown in FIG. 4, the mandrel 10includes the tensioning device 20 and tensioning groove 40 adjacent tothe anchoring device 30 and anchoring groove 50 and the tensioningdevice 22 and tensioning groove 42 adjacent to the anchoring device 32and anchoring groove 52. In this regard, the mandrel 10 may include anysuitable number of tensioning devices and tensioning grooves and thesetensioning devices and tensioning grooves may be located at any suitablelocation. Suitable locations include those locations disposed betweenthe fastened ends of the preform 100. In particular, suitable locationsmay be disposed relatively close to the anchoring grooves and devices50, 52, 30, and 32 to minimize scrap production.

FIG. 5. shows a cross-section of another embodiment of the disclosure.The mandrel 10 may be provided, as with the example shown in FIG. 1,with a preform 100 laid thereon. The preform 100 may include anysuitable composite material, for instance a bi-axial braided compositeweave and the like. In this instance, again for example, a braided ornear net form layer is shown placed prior to impregnation with a resin.

Extending from an end of the preform 100 may be a wire 200. The wire 200may be coupled to a tensioning device 20, herein shown as a wiretensioning device. An optional clamping device 250 may clamp the preform100 and provide a means of attaching the wire 200 to the preform 100.The tensioning device 20 draws the wire 200 and thereby translatestension through the clamping device 250 and to the preform 100. Thetensioning device 20 draws tension on the wire 200 and thus stretches ordraws taut the layers of the preform 100. The mandrel 10 may include ananchoring groove 50 which accommodates an anchoring device 30, a taperedblock and clamp for example. Alternatively, both ends of the preform 100may be coupled through respective clamping devices 250 and wires 200 torespective tensioning devices 20, and thus tensioned through both endsof the preform 100.

The tensioning device 20 may be incorporated as part of the mandrel 10,within the mandrel 10, or as a separate device from the mandrel 10. Theanchoring device 30 and the tensioning device 20 may be applied to holdthe preform 100 on the mandrel 10 using the vacuum bag 60. Thetensioning device 20 may stretch out, draw taut or otherwise aids inremoving both the observed and unobserved aberrations, voids, wrinkles,and the like through the tensioning of the wire 200. Alternatively, thetensioning device 20 can be applied to hold the preform 100 withoutdeparting from the spirit of the disclosure.

Although an example of the device is shown using a braided preform, itwill be appreciated that other preforms can be used. Also, although thedevice may be useful to draw tension in preforms of braided material itcan also be used to draw tension in any suitable preform.

An example embodiment of a mandrel 610 is shown in FIG. 6. Preform 700,anchoring device 630, block 654, clamp 634 and vacuum bag 660 are notshown for clarity. The preform 700 may be laid up on the mandrel 610.Mandrel 610 may be shaped to form at least a part of a fuselage sectionpreform 700 or a wing section preform 700. Mandrel 610 may have at leastone edge. Mandrel 610 may have at least one anchoring groove 650 neareach edge. Mandrel 610 may have at least one tensioning groove 640 neareach anchoring groove 650. FIG. 6 shows the mandrel 610 as beinggenerally curved. However, in other examples, the mandrel 610 need notbe curved or may be curved and/or twisted in any suitable manner. In aparticular example, the mandrel 610 may be curved at a radius of about75 inches to about 360 inches. In other examples, the mandrel 610 mayinclude a configuration suitable to fabricate a tapering fuselage orwing section.

FIG. 7 show a cross-section illustration of mandrel 610 with preform700, anchoring device 630, block 654, clamp 634 and vacuum bag 660added. The preform 700 is shown inside the vacuum bag 660. At a first orproximal end, the preform layers 701-705 may be anchored by theanchoring device 630 and anchoring groove 650. In addition, a distal endof the preform 700 may be secured to the mandrel 610 by the block 654and clamp 634. In this regard, the block 654 and clamp 634 and theanchoring device 630 and anchoring groove 650 may be generally describedas fasteners. That is, for example, the block 654 and clamp 634 functiontogether to fasten or secure the preform 700 to the mandrel 610 in asimilar manner as the anchoring device 630 and anchoring groove 650.

Additionally, embodiments of the disclosure are not limited to the block654 and clamp 634 and the anchoring device 630 and anchoring groove 650,but rather, any suitable fastener may be included in various embodimentsof the disclosure. Suitable fasteners include, at least, clamps,presses, and the like. Furthermore, suitable fasteners may includeaffixing, chemical or heat welding, and the like.

The preform layers 701-705 may include any suitable composite materialsuch as braided preforms, layers of prepreg, foil, film, fabric,unidirectional tape, and the like or any combination thereof. FIG. 7show a single tensioning device 620 and tensioning groove 640 which doesnot limit the number of tensioning devices 620 or grooves 640 that maybe utilized nor does the incorporation of either element in the mandrel610 limit the respective tensioning device or groove from beingincorporated in a multi-part mandrel 610. The tensioning device 620 mayfurther include a clamp or actuator 628 to urge the tensioning device620 towards the tensioning groove 640.

The tensioning groove 640 and the preform layers 701-705 may be engagedby the tensioning device 620, here shown as a tapered block and clamp.Clamping layers 701-705 into the tensioning grooves applies tensionforces substantially across the cross section of the preform 700 and thepreform layers 701-705. This effectively “pulls” excess material out ofthe preform 700 and stretches out or draws taut wrinkles or otheraberrations.

It is an advantage of this and other embodiments of the disclosure thatthe tension generated by the tensioning device 620 and tensioning groove640 is essentially spread through the preform 700. As a result, thepreform 700 may be drawn down onto the mandrel 610. Furthermore, inlayered preforms 700, each layer 701-705 of the preform 700 may besubjected to essentially the same tension which may reduce internalaberrations.

Also shown in FIG. 7, a net trim line 670 and 672 indicate net ends of acomposite item 680. That is, following resin infusion and/or resincuring, the composite item 680 may be generated by cutting or trimmingat the net trim lines 670 and 672.

The many features and advantages of the embodiments are apparent fromthe detailed specification, and thus, it is intended by the appendedClaims to cover all such features and advantages of the embodimentswhich fall within the true spirit and scope of the disclosure. Further,since numerous modifications and variations will readily occur to thoseskilled in the art, it is not desired to limit the disclosure to theexact construction and operation illustrated and described, andaccordingly, all suitable modifications and equivalents may be resortedto, falling within the scope of the embodiments.

What is claimed is:
 1. An apparatus for tensioning a preform,comprising: a mandrel to receive a preform and having a mandrel surface,the mandrel having four mandrel edges, the preform having preform edges;an anchoring groove formed on the mandrel surface and disposed near eachone of the four mandrel edges; an anchoring device being configured andlocated to urge a preform edge towards at least one of the anchoringgrooves to secure the preform edge therebetween; a first tensioninggroove formed on the mandrel surface and disposed along a first mandreledge; a first tensioning device being configured and located to urge atleast a portion of the preform into the first tensioning groove and themandrel surface being substantially planar or having a single curvatureor a single twist along a length of the mandrel surface between thetensioning groove and the anchoring groove with no intervening groovestherebetween.
 2. The apparatus of claim 1, further comprising a vacuumbag enclosing at least the preform on to the mandrel.
 3. The apparatusof claim 1, wherein the mandrel is twisted along an axis.
 4. Theapparatus of claim 1, wherein the mandrel is a curved mandrel.
 5. Theapparatus of claim 1, further comprising: a second tensioning groovedisposed along a second mandrel edge; and a second tensioning devicecooperatively coupled to the second tensioning groove, the secondtensioning device being configured to urge a portion of the preform intothe second tensioning groove to further increase an amount of tension inthe preform.
 6. The apparatus of claim 1, wherein the tensioning deviceis a tapered block.
 7. The apparatus of claim 1, further comprising: asecond anchoring groove disposed along a second mandrel edge; and asecond anchoring device cooperatively coupled to the second anchoringgroove, the second anchoring device being configured to urge the secondpreform edge towards the second anchoring groove to secure the secondpreform edge therebetween.
 8. The apparatus of claim 1, furthercomprising: a clamp disposed at the second mandrel edge, the clamp beingconfigured to urge a second preform edge towards a second mandrel edgeto secure the second preform edge therebetween.
 9. The apparatus ofclaim 1, wherein the anchoring device is a tapered block.